1. Field of the Invention
This invention relates generally to wellbore core sampling apparatus and methods, and more particularly to an advanced coring system and method utilizing a core height measurement module that accurately measures the amount of core captured as a function of time and depth, a data telemetry-module that conveys this information to the surface in real time, and a full closure valve assembly that completely closes the bottom of the core barrel under surface control to prevent loss of unconsolidated and highly fractured cores.
2. Brief Description of the Prior Art
The taking of core samples is the most accurate means to evaluate rock properties for hydrocarbon and ore body development, scientific investigation and environmental clean up activities. Conventional coring methods and apparatus have two major shortcomings: (1) the absence of real-time monitoring of the core length (recovery) in the core barrel, and (2) the lack of complete closure of the core barrel opening to prevent core loss. While partial or complete core loss is generally not a problem in competent formations, it is an important problem in unconsolidated and highly fractured ones. A review of U.S. and Canadian coring activities showed that partial core loss is experienced in approximately 20% of the wells cored. This lost core translates into considerable costsxe2x80x94particularly in offshore drilling operations where rig rates can run in excess of $10,000 per hour. Of even greater potential importance is the loss of geologic information.
It is extremely important to recover the entire interval where the rock is being cored. If any core is not recovered, valuable information is lost. Coring operations are performed under a wide range of operating conditions. These include: (1) variation in wellbore inclination angle from zero (vertical) to ninety degrees (horizontal), (2) use of wide range of drilling fluids such as water and oil-based mixtures, nitrooelltited muds, and air/foam mists, (3) encountering zones of lost circulation and (4) rapid changes in lithology. The net result of these conditions in the standard coring process introduces uncertainties which occur because standpipe pressure, pump speed, mud weight and drill cutting returns (among other things) at the surface are used to xe2x80x9cassessxe2x80x9d the progress of the coring operation. None of these parameters are direct measures of the amount of core actually being recovered in the barrel. The present invention eliminates these uncertainties by providing a real-time monitoring device.
The monitoring feature of the present system accurately measures the amount of core captured as a function of time and depth, and conveys this information to the surface in real combined with the ability to completely close the bottom of the core barrel under surface control and prevent loss of unconsolidated and highly fractured cores, the present system will improve coring success and reduce overall coring costs.
The present invention provides new hardware modules for core height measurement and core barrel closure that are compatible with conventional and wireline-retrievable coring systems. This present system also does not require any changes to the standard inner and outer core barrel assemblies and it operates with both sealed oil-lubricated and mud-lubricated bearing packs.
A suitable ball valve assembly for use with the present invention is disclosed in U.S. Pat. No. 6,009,960 titled Coring Tool, issued Jan. 4, 2000 and assigned to Diamond Products International, Inc., of Houston, Tex., which is hereby incorporated by reference to the same extent as if fully set forth herein. U.S. Pat. No. 6,009,960 does not disclose the present electromagnetic ranging system for core height measurement as a function of time and depth, or the present data telemetry system that conveys this information to the surface in real time, however, preliminary testing of the combination utilizing such a valve assembly has proven satisfactory.
The present invention is distinguished over the prior art in general by an advanced coring system and method utilizing a core height measurement module that accurately measures the amount of core captured as a function of time and depth, a data telemetry module that conveys this information to the surface in real time, and a full closure valve assembly that completely closes the bottom of the core barrel under surface control to prevent loss of unconsolidated and highly fractured cores. The transmitter of the electromagnetic ranging system rides atop a core sample being formed in the barrel chamber and a receiver member of the electromagnetic ranging system is fixed at a top end of the barrel a known distance above the transmitter. During the coring operation the transmitter transmits a fixed frequency signal to the receiver through drilling fluid disposed therebetween. The distance between the transmitter and receiver decreases and the amplitude of the transmitted signal changes as a function of the separation distance between the transmitter and receiver as the core sample enters the inner barrel and the height of the core sample within the barrel is determined as a function of time and depth. The pressure of the drilling fluid is modulated to transmit a series of pressure pulses from the barrel to the surface encoded to produce a binary digital or pulse-width modulation signal. The electromagnetic ranging system may be incorporated into a coring tool having a core bit disposed at a lower end and a full closure ball valve and core retention assembly movable to a closed position to close the bottom end of the inner barrel and prevent the loss of core collected in the inner barrel chamber.
It is therefore an object of the present invention to provide an advanced coring system and method which will eliminate uncertainties that may occur due to variations in standpipe pressure, pump speed, mud weight and drill cutting returns, among other things.
It is another object of this invention to provide an advanced coring system and method utilizing a core height measurement module that produces direct accurate measurement of the amount of core actually being recovered in the barrel of the coring tool.
Another object of this invention is to provide an advanced coring system and method that conveys accurate core height data of the core being recovered in the barrel of the coring tool to the surface in real time.
Another object of this invention is to provide an advanced coring system and method that will prevent loss of unconsolidated and highly fractured cores.
Another object of this invention is to provide an advanced coring system and method utilizing core height measurement modules and core barrel closure modules that are compatible with conventional and wireline-retrievable coring systems.
A further object of this invention is to provide an advanced coring system and method utilizing core height measurement modules and core barrel closure modules that does not require any significant changes to standard inner and outer core barrel assemblies and will operate with both sealed oil-lubricated and mud-lubricated bearing packs.
A still further object of this invention is to provide an advanced coring system and method which will improve coring success and reduce overall coring costs.
Other objects of the invention will become apparent from time to time throughout the specification as hereinafter related.
The above noted objects and other objects of the invention are accomplished by an advanced coring system and method utilizing a core height measurement module that accurately measures the amount of core captured as a function of time and depth, a data telemetry module that conveys this information to the surface in real time, and a full closure valve assembly that completely closes the bottom of the core barrel under surface control to prevent loss of unconsolidated and highly fractured cores.